"In the long run, it's not a question of whether they deserve to be forgiven. You're not forgiving them for their sake. You're doing it for yourself. For your own health and well-being, forgiveness is simply the most energy-efficient option. It frees you from the incredibly toxic, debilitating drain of holding a grudge. Don't let these people live rent free in your head. If they hurt you before, why let them keep doing it year after year in your mind? It's not worth it but it takes heart effort to stop it. You can muster that heart power to forgive them as a way of looking out for yourself. It's one thing you can be totally selfish about." -HeartQuotes
...and more importantly -
"For if you forgive others their trespasses, your heavenly Father will also forgive you, but if you do not forgive others their trespasses, neither will your Father forgive your trespasses."
- Matthew 6:14-15